Evolution
Evolution in biology is a genetic change in a line of descent over time. The evolution of life on Earth has resulted in many hundreds of thousands of species. Genetic evidence reveals that humans share a common ancestor with life forms as different from us as bacteria and corn plants. In early 1800s, the source of Earth’s remarkable diversity of life forms was hotly disputed. Many people believed that all species had come into existence at the same time in the distant past. In 1831 Charles Darwin sailed to South America, and during the long Atlantic crossing Darwin studied geology and collected marine life. During stops along the coast and at various islands, he observed other species of organisms in environments ranging from sandy shores to high mountains. Darwin’s melding of his observations of the natural world with the ideas of others led him to propose that evolution could occur by way of a process called natural selection. The history of life on Earth spans nearly 4 billion years. It is a story of how species originated, survived or went extinct, and stayed put or spread into new environments. Microevolution is the name for cumulative genetic changes that may give rise to new species, Macroevolution is the name for the large-scale patterns, trends, and rates of change among groups of species. An individual fish, flower, or person does not evolve. Evolution occurs only when there is change in the genetic makeup of whole populations of organisms. In biology, a population is a group of individuals of the same species occupying a given area. In theory, the members of a population have inherited the same number and kinds of genes. These genes make up the population’s gene pool. Mutation is harmful when it alters a trait such that an affected individual cannot survive or reproduce as well as other individuals. For example, for us humans, small cuts are common. By contrast, a beneficial trait improves some aspect of an individual’s functioning in the